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Commit optional code for high-precision EQ which will almost certainly not make a difference on 16 bit output targets.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@12451 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Thom Johansen 2007-02-22 13:55:49 +00:00
parent 6c3db6e65f
commit c4ccd9ee86
2 changed files with 72 additions and 32 deletions
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64
apps/eq_arm.S
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@ -7,7 +7,7 @@
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2006 Thom Johansen
* Copyright (C) 2006-2007 Thom Johansen
*
* All files in this archive are subject to the GNU General Public License.
* See the file COPYING in the source tree root for full license agreement.
@ -17,6 +17,15 @@
*
****************************************************************************/
/* uncomment this to make filtering calculate lower bits after shifting.
* without this, "shift" of the lower bits will be lost here.
*/
/* #define HIGH_PRECISION */
/*
* void eq_filter(int32_t **x, struct eqfilter *f, unsigned num,
* unsigned channels, unsigned shift)
*/
.text
.global eq_filter
eq_filter:
@ -33,35 +42,40 @@ eq_filter:
ldr r14, [sp, #8] @ r14 = numsamples
ldmia r10, { r0-r3 } @ load history, r10 should be filter struct addr
str r10, [sp, #4] @ save it for loop end
.loop:
/* r0-r3 = history, r4-r8 = coefs, r9 = x[], r10..r11 = accumulator,
r12 = shift amount, r14 = number of samples.
See eq_cf.S for explanation of what this loop does. Primary difference
is the reordering of the equation we do here, which is done for register
reuse reasons, we're pretty short on regs.
* r12 = shift amount, r14 = number of samples.
*/
smull r10, r11, r6, r1 @ acc = b2*x[i - 2]
mov r1, r0 @ fix input history
smlal r10, r11, r5, r0 @ acc += b1*x[i - 1]
ldr r0, [r9] @ load input and fix history in same operation
smlal r10, r11, r4, r0 @ acc += b0*x[i]
smlal r10, r11, r7, r2 @ acc += a1*y[i - 1]
smlal r10, r11, r8, r3 @ acc += a2*y[i - 2]
mov r3, r2 @ fix output history
mov r2, r11, lsl r12 @ get result
@ TODO: arm makes it easy to mix in lower bits from r10 for extended
@ precision here, but we don't have enough regs to save the shift factor
@ we would need (32 - r12).
str r2, [r9], #4 @ save result
subs r14, r14, #1 @ are we done with this channel?
.loop:
/* Direct form 1 filtering code.
* y[n] = b0*x[i] + b1*x[i - 1] + b2*x[i - 2] + a1*y[i - 1] + a2*y[i - 2],
* where y[] is output and x[] is input. This is performed out of order to
* reuse registers, we're pretty short on regs.
*/
smull r10, r11, r6, r1 @ acc = b2*x[i - 2]
mov r1, r0 @ fix input history
smlal r10, r11, r5, r0 @ acc += b1*x[i - 1]
ldr r0, [r9] @ load input and fix history in same operation
smlal r10, r11, r4, r0 @ acc += b0*x[i]
smlal r10, r11, r7, r2 @ acc += a1*y[i - 1]
smlal r10, r11, r8, r3 @ acc += a2*y[i - 2]
mov r3, r2 @ fix output history
mov r2, r11, asl r12 @ get upper part of result and shift left
#ifdef HIGH_PRECISION
rsb r11, r12, #32 @ get shift amount for lower part
orr r2, r2, r10, lsr r11 @ then mix in correctly shifted lower part
#endif
str r2, [r9], #4 @ save result
subs r14, r14, #1 @ are we done with this channel?
bne .loop
ldr r10, [sp, #4] @ load filter struct pointer
stmia r10!, { r0-r3 } @ save back history
ldr r11, [sp, #12] @ load number of channels
subs r11, r11, #1 @ all channels processed?
ldr r10, [sp, #4] @ load filter struct pointer
stmia r10!, { r0-r3 } @ save back history
ldr r11, [sp, #12] @ load number of channels
subs r11, r11, #1 @ all channels processed?
strne r11, [sp, #12]
bne .filterloop
add sp, sp, #16 @ compensate for temp storage
add sp, sp, #16 @ compensate for temp storage
ldmia sp!, { r4-r11, pc }